CDC: Antibody test results are often wrong and should not be relied on

• The CDC has released new guidance stating the results of antibody tests are wrong half the time. 
• The agency also said that antibody tests shouldn't be used to make important decisions about re-opening.
• The Food and Drug Administration has also said that antibody tests are not reliable.
• Visit Business Insider's homepage for more stories.

The CDC has released new guidance on antibody tests, warning that they can be wrong half the time and shouldn't be used to inform important policy decisions.

The antibody test, also known as a serologic test, is a blood test that checks the body to see if it has antibodies that can fight COVID-19, and can help people figure out if they had COVID-19 and recovered.

The immune system creates antibodies to fight disease, and often these antibodies remain in the body after recovery, and can be donated to people currently fighting coronavirus.

But this medical test is often inaccurate. Sometimes the test can result in a false positive, wrongly suggesting a patient does have coronavirus-fighting antibodies, or a false negative.

"Serologic test results should not be used to make decisions about grouping persons residing in or being admitted to congregate settings, such as schools, dormitories, or correctional facilities," it says on the CDC website. "Serologic test results should not be used to make decisions about returning persons to the workplace."

Previously, employers had been considering relying on these tests to determine when people could head back into workplaces, while hundreds of companies rushed to create their own version of the tests and hospitals offered these tests to healthcare workers, children, and anyone who wanted them.

But even when these often-unreliable tests gave people a positive result, that wasn't something that carried any weight during a pandemic.

"Even when you log on to your healthcare portal, and it says, 'Congratulations, you are positive for Covid antibodies,' meaning you ostensibly have some immunity, it's not like something you can take to the bank," Dr. Andrew Noymer, a public health associate professor at the University of California Irvine, previously told Insider.

There is still a lot researchers don't understand about COVID-19 and antibodies

Molly DeMellier, a 27-year-old girl who survived COVID-19, tried to donate blood to the Mount Sinai antibody trial. She assumed that since she survived the novel coronavirus, her body had produced antibodies that she could donate for other people sick with the disease. At Mount Sinai, she discovered she barely had enough antibodies to donate, raising more questions about the nature of antibodies and their possible use, Insider's Julia Naftulin previously reported.

"As with anything else in medicine, that there is probably a variable response that people's bodies have to this virus," Dr. David L. Reich, President and Chief Operating Officer of Mount Sinai, previously told Insider. "And it's unclear if it has anything to do with severity of disease or other factors because it's just way too soon in the history of this disease to have figured that out."

Millions of antibody tests, produced by hundreds of companies, are flooding the American market. The FDA, which originally rushed to approve antibody tests, implemented a tougher testing system on May 4 after the accuracy of those tests were called into question.

"It's a disaster. These tests are not worth anything, or have very little use," one CEO said, according to a recording provided to Business Insider by the company.